In electromotive drives, stepped speed control is implemented using a resistor circuit. During operation, electrical energy is converted into thermal energy by said resistor circuit. This thermal energy may have a negative effect on the electromotive drive in respect of its service life. Overheating of the drive and increased drive component wear may occur. If the resistor circuit is disposed inside the motor, an air flow suitable for cooling cannot generally be guaranteed. This leads to an unwanted heat concentration in sections of the resistor circuit or in the drive as a whole, which may ultimately result in component failure.
To dissipate or remove the thermal energy produced, a known solution is to use cooling fins, large-area heatsinks or supplementary ventilation. Another known solution is to increase the service life by using more temperature-resistant, more durable and therefore more costly drive components.
DE 101 29 234 A1 discloses an electric drive unit comprising a gear housing, a motor housing, a separately implemented, watertight-sealed electronics housing, a brush holder and a signal receiver disposed on said brush holder. The brush holder is provided with plug contacts to which electronics provided in the electronics housing are electrically connected. In addition, the brush holder is fixed to the motor housing at the transition between the motor housing and the gear housing. No references to any kind of cooling measures are to be found in DE 101 29 234 A1.